1. Field of the Invention
The present invention relates to an image sensor used for scanners or bill discriminators.
2. Description of the Related Art
In a one-dimensional scanning line image sensor, it is universal taking arrangements in which a document is irradiated from a plurality of directions in order to ensure a reading performance of the document waving due to such as rumples. For example, JP-A2006-014081 (see Patent Document 1) discloses, in FIG. 1, an image reader equipped with a lighting apparatus 3 irradiating light to a reading position of a document from both sides thereof.
Further, JP-A2004-048290 (see Patent Document 2) discloses, in FIG. 1, an image sensor including a light source 2 illuminating an illuminated object O; and a reflecting member 4 that is disposed at a position opposed to the light source 2 and directs part of the light from the light source 2 toward the illuminated object O so as to rationalize a balance of the quantity of light to direct light from a light source using an auxiliary reflecting mirror, and cancel a shadow; wherein shielding members 9,9′ are provided between the light source 2 and the illuminated object O, and between the reflecting member 4 and the illuminated object O, and the shielding members 9, 9′ shield irradiated light from the light source 2 and reflected light from the reflecting member 4 at a fixed rate.
Furthermore, JP-A07-319082 (see Patent Document 3) discloses, in FIG. 1, a lighting apparatus of an image forming device in which a second sub-reflector 7c is elastically deformably provided in a thickness direction to simplify an arrangement which adjusts the quantity of light impinging on a document from a bar-shaped light source, and the quantity of light from a light source 5 striking on the document is adjusted by displacing the second sub-reflector 7c by rotation of a screw shaft 12.
Moreover, JP-A2003-348299 (see Patent Document 4) discloses, in FIG. 1, a line lighting apparatus which includes a light-emitting face 17 emitting light incident on a square bar-shaped light-guiding element 1 from a light source 2 to a corner along a longitudinal direction of the light-guiding element 1; light scattering patterns being not provided at an area in the vicinity of the light source 2, out of two sides where the reflected quantity of light incident on the light-emitting face 17 becomes maximum; light scattering patterns 18b being provided at an area remote from the light source; and light scattering patterns 18a being provided at an area to the light source in at least one side, out of two sides orthogonal to a side where the quantity of reflected light becomes maximum. This prevents a shortage of the quantity of light from an area in the proximity of the light source 2, which precludes the non-uniform emitting quantity of light from the light-emitting face 17 along a longitudinal direction of the light-guiding element 1.
Patent Document 1: JP-A2006-014081 (FIG. 1)
Patent Document 2: JP-A2004-048290 (FIG. 1)
Patent Document 3: JP-A7-319082 (FIG. 1)
Patent Document 4: JP-A2003-348299 (FIG. 1)
However, although the image reader described in the Patent Document 1 achieves image formation of a clear image even when a document is partially lifting, the image reader must build in a linear lighting apparatus in each side of the document. Consequently, the image reader rises in price.
Further, in the image sensor described in the Patent Document 2, a reflecting member is provided opposed to the light source such as a halogen lamp, and a shielding member is provided on an under surface of a light-transmitting member, thus shielding irradiated light from the light source 2 and reflected light from the reflecting member at a certain ratio. However, the provision of the shielding member incurs a loss of illuminating light, which decreases luminous intensity on a surface of the document and impairs efficiency.
Furthermore, in the lighting apparatus described in the Patent Document 3, the quantity of light from the light source 5 impinging on the document can be adjusted as a dimmer plate is displaceable in a swinging manner in a direction where a free end of the plate draws near to or goes away from a document by using second sub-reflectors. However, each of the second sub-reflectors demands mechanical adjustment at the time of adjustment of the quantity of light, thus complicating the adjustment.
In the linear lighting apparatus described in the Patent Document 4, light scattering patterns are formed to the main face (the side where reflected light becomes maximum) of the bar-shaped light-guiding element of which section including the light-emitting face is pentagonal, and at the same time, to the side adjacent to the main face of one end of the light source. The labors for uniformity of the quantity of emitted light; however, this apparatus includes only a one-side light source. Accordingly, the Patent Document 4 makes no mention of insuring a reading performance of a document waving due to such as rumbles, as is demonstrated by the present invention.